The present invention relates to machines and equipment for exercising the muscles of the human body and, more in particular, it concerns a device for selectively varying, in a mechanical transmission, connecting a movement organ receiving a muscle action of a person performing the exercise and resistive means that oppose said muscle action, the forces and the movements exchanged between the movement organ and the resistive means.
The prior art concerning exercise machines and equipment provides for the use, as resistive means that oppose the muscle actions of the person who performs the exercise, of the weights connected to the movement organ by means of a cable, appropriately routed along a path determined by a series of pulleys variously located on the structure of the machine.
The weights are constituted by stacks of vertically superposed elements, which are selected in variable number according to the need of the person who performs the exercise. In such machines, loads may vary in intensity, by discrete quantities, according to multiples of the unit weight of each component of the stack and with the selection, on each occasion, of a greater or smaller number of components of the stack.
The aim of the present invention is to allow to vary the resistive load opposing the movement organ, without requiring a variation of the conformation of the set stack of weights, or of the number of components of the stack already selected.
In accordance with the invention, this aim is achieved by a device for selectively varying, in a mechanical transmission of an exercise apparatus connecting a movement organ receiving a muscle action of a person performing the exercise and resistive means that oppose said muscle action, the forces and the movements exchanged between said movement organ and said resistive means, characterized in that it comprises at least a pulley; a movable structure bearing a pivot pin for the rotation of the pulley, to which structure is applied a traction force correlated to the muscle effort which the person performing the exercise applies to said movement organ, said traction force being coplanar with, and directed transversely to, the axis of the rotary pin of the pulley; a cable element wound around an arc of the pulley in such a way as to form a pair of parallel branches, a first branch whereof has an end connected to the resistive means, the second branch instead having an end connected to a bar movable within a vertical guide; said device further comprising means for selectively fastening the movable bar and the fixed guide; said fastening means anchoring, in a first operative condition, the movable bar to the fixed guide, thereby opposing, to the traction force applied to the pivot pin of the pulley, a reaction force that is twice the reaction force of the resistive means; said fastening means leaving instead, in a second operative condition, the bar free to translate relative to the guide until it reaches a condition of abutment against the movable support structure, in which the traction force applied to the pivot pin is opposed by a reaction force equal to the reaction force of the resistive means.